This invention relates to an information transmission system comprising a first transmitter/receiver and a plurality of further transmitter/receivers which can each communicate with the first transmitter/receiver over the same transmission channel or group of transmission channels.
An example of such a system is a trunked mobile radio transmission system in which the first transmitter/receiver is a base or central control station and the further transmitter/receivers are the various mobile radios, the number thereof being larger than the number of radio channels available. If only radio access is required the base station in such a system may, in addition to its system control function, act only as a multichannel repeater. If land line connections are also required the base station will also have to include means for connecting any of the land lines to any of the radio channels. In order to enable the base station to perform its control function facilities must be provided for signalling to occur between the various mobile radios and the base station when a call is requested and a channel is assigned for that call. In small such systems (in which for example a number of channels between 1 and 5 is available) it is inefficient to assign one channel for signalling permanently, and in such systems it is preferably arranged that all channels can be used both for signalling and for speech.